Stepping motor control system

ABSTRACT

A stepping motor control system for motors having at least two poles with each pole having a bifilar winding with two input points wherein power is selectively applied to the two input points in accordance with a predetermined sequence.

United States Patent Rosen 51 Mar. 7, 1972 [54] STEPPING MOTOR CONTROLSYSTEM 3,328,658 6/1967 Thompson ..318/ 138 3,354,367 11/1967Stockebrand 318/138 [72] Oak Park 3,411,058 11/1968 Madsen e181...318/138 [73] Assignee: The Babcock 8: Wilcox Company, New 3,445,7415/1969 Gerber ..3l0/49 X York, NY. 3,461,365 8/1969 Newland et al.318/138 X 3 476 996 11/1969 Fredriksen ..3l8/l38 29, l [22] Dec 9693,523,230 8/1970 York ..318/138 X 211 Appl. No.: 888,648

, Primary Examiner-G. R. Simmom [52 us. 01 ..3l8/696, 318/138Niamey-Barnes, Kimlle, him/Whom [51] Int. Cl. "02k 37/00 [58] Field ofSearch ..318/138, 254, 696, 685; ABSTRACT 310/49 A stepping motorcontrol system for motors having at-least two poles with each polehaving a bifilar winding with two [56] References Cited input pointswherein power is selectively applied to the two UNITED STATES PATENTSinput points in accordance with a predetermined sequence.

3,239,738 3/1966 Welch ..3l0/49 X 2 Claims, 16 Drawing Figures STARTCYCLE f 2 I HIGH RESOLUTION INTERPOLATOR 1 sun: 111 Og gg 1 POWER lINTERPL. Manama DRIVER Amman L 1 l 1- Couwi' not ended 26 H1 L0 27 28Enable CoMsTAN-r' FLIP CURRENT FLPP 0 1.0 Power Supplq Patented March 7,1972 3,648,144

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INVENTOR.

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INVENTOR. 'PHILIP J. ROSEN BY am M MP M ATTORNEYS STEIPING MOTOR CONTROLSYSTEM This invention relates to stepping motors and particularly tostepping motor control circuits.

BACKGROUND OF THE INVENTION It has become common in the control ofmechanical systems to employ what is known as a stepping motor. This isan electric motor, often with 100 electrical poles, and with permanentmagnet poles on the rotor. One type of such motor is wound as atwo-phase synchronous motor, using a bifilar winding.

These motors are synchronous so that some method is provided to makecertain that there is no accumulated slip between rotor position and theposition of the driving magnetic vector. Since the slip usually resultsfrom the ability of induced rotor poles to move continuously over thesurface of the rotor, the usual method is to provide immovable poles byusing sliprings and an externally excited DC rotor magnetic field orelse permanent magnets in the rotor. The stepping motors of the presentinvention use permanent magnetic rotors.

Among the objects of the present invention are to provide a controlcircuit and method of controlling a stepping motor of the aforementionedtype in a special mode in order to obtain a greater number of steps perrevolution; wherein such control is achieved without changing thestructure of the motor; and wherein control can be selectively appliedto operate the motor in the conventional mode or in the special modewith the plurality of added steps.

DESCRIPTION OF THE DRAWINGS FIGS. 1-5 are schematic diagrams of priorart motors to which the invention is directed.

FIG. 6 is a pulse diagram of the operation of the prior art motors.

FIG. 7 is a schematic diagram of the manner of excitation of a motor inaccordance with the invention.

FIG. 8 is a pulse diagram showing the manner in which pulses can beapplied in accordance with the invention.

FIG. 9 is a schematic wiring diagram of the motor windings in accordancewith the invention.

FIG. 10 is a vector diagram of the motor in one mode of operation inaccordance with the invention.

FIG. 11 is a vector diagram of the motor in accordance with another modeof operation.

FIG. 12 is a schematic diagram of a control circuit in accordance withthe invention.

FIG. 13 is a more specific diagram of the control circuit shown in FIG.12.

FIGS. 14 and 15 are pulse diagrams of the functioning of the, controlcircuit shown in FIG. 13.

FIG. 16 is a schematic diagram of a modified form of control circuit.

DESCRIPTION Although the terms two-phase synchronous motor, using abifilar winding are well understood, for the sake of clarity in laterexposition their precise meaning will be briefly reviewed. A two-phasemotor has two windings or sets of windings, connected so as to be drivenby two AC sources which are approximately 90 out of time phase with eachother. It should be understood that there may be more than one pair ofpoles in the winding. When a full cycle of AC excitation is applied toboth windings, the resultant magnetic vector moves smoothly over theangle separating one pole pair from the next. FIG. 1 shows such awinding and FIG. 2 a common method of excitation. The rotor of such amachine has magnetic poles which follow the magnetic vector to producerotation.

It is possible to provide a means of reversing the magnetic vectorslocation in space without reversing the polarity of the excitation. Thisis done by winding the two basic windings in pairs. That is, the wire islooped double and then the winding is set in place two wires at a timeas the two ends arespooled out. The loop is then cut in the center andone loop wire is brought out as a winding end, one end wire is broughtout as a winding end and the other end wire is spliced to the other loopwire to serve as the center. This is done on both windings and thecenters are joined; one common wire being brought out. The connectionsare shown in FIG. 3. We may now excite the system either with a bipolarsource, as before, or with voltage of a single polarity. Considerbipolar sources first. Since the actual common point 2, the junction ofall four windings, is buried in the structure and only a single wire isbrought out; only half of the winding (FIG. 4) can be used in thesynchronous mode with bipolar sinusoidal excitation.

Because of the fact that the rotor is made with permanent magnetic polesinstead of the induced poles normally employed with continuous-rotationmotors, the motor connected as shown in FIG. 4, but excited with asquare wave rather than a sine wave will move at the same average speed,but will step rather than move continuously. Of course, the phaseshifting network does not work very well with square waves-one wouldordinarily provide two sources of square waves, apart in time phase asshown in FIGS. 5 and 6.

Alternatively, a single source of DC voltage can be switched into theseveral windings at will. FIG. 7 shows the situation. The open state ofa switch is represented as zero and the closed state as l in theassociated tabulation, and arbitrarily assume an initial state. Inaccordance with the prior art, as discussed in U.S. Pat. No. 3,117,268,one winding is switched at a time. That is, power may be switched from Ato B or from C to D, but not from A to C or B to D in a given step. Atypical sequence is given below:

It will be noted that this switching sequence is merely a sort ofliteral translation of sinusoidal excitation of two 90 windings intodiscrete terms. Thus the behavior of the motor in the stepping mode isdirectly analogous to that in the synchronous mode.

The method by which this sequence of excitations produces steps isdiscussed in detail in the aforementioned U.S. Pat. No. 3,117,268. Ineffect in a cycle of excitation as shown in Table l, the motor moves onefull cycle, that is, through a pair of electrical poles. Each step movesthe rotor through 90 electrical degrees. Clearly, therefore, with a polemotor, 200 steps per revolution are produced and 50 full cycles ofelectrical switching per revolution. FIG. 8 shows the waveforms.

Basically, in accordance with the invention, the motor of the two-phasesynchronous type, utilizing bifilar windings is operated in accordancewith the following rules: Excitation can be switched between bifilarwound pairs and only one bifilar winding can be switched during anystep. Thus, A can be turned off and B turned on, but not A oh and C oh"in one step. In accordance with the above guidelines or rules, theinvention contemplates operation of the motor in accordance with thefollowing mode or cycle:

TABLE 2 State A 0 Major 0 0 Minor 0 l Major l l Minor l 2 Major l 2Minor 0 (Old state 0) (Old ltate l) (Old state 2) 3 Major 1 The vectordiagram shown in FIGS. 10 and 11 show the relationship of operation ofthe motor in a conventional mode (FIG. 10) and in accordance with themode of Table 2 (FIG. 1 l

It can be seen that by this arrangement four intermediate states areprovided halfway between the major states of the conventional mode andthat these states are actual stable obtainable states. It can be seenfurther that for purposes of convenience, the states are identified asmajor corresponding to the conventional mode and minor corresponding tothe intermediate states.

It can further be appreciated that the additional steps that areproduced are made at a sacrifice of output torque because the four minorstates are operating at only half power. Furthermore, the two groups A,B and C, D are no longer accurately 90 out of time phase. The overallresult is that there is an approximate 20 percent loss of torque.However, the additional steps are achieved permitting more accuratecontrol.

FIG. 12 is a block diagram of a circuit for continuous excitation withthe choice of 200 or 400 steps per revolution and of forward or reversesequence. A two-line binary input controls direction. An input triggerselector steers the input trigger signal as function of the selection ofthe high or normal resolution mode. The resulting clock output drives atranslator 2, which has a reversing capability, and which directs thestate interpolator 3 as to the order in which the states should progresscorresponding to forward or reverse. The state interpolator outputdrives the high-low resolution selector 4 which determines whether theadditional states described above will or will not be used. Thusproducing high-resolution or lowresolution behavior of the motor. Theactual output states are controlled by selector 4 and translator 2,being generated in driver 5.

We will discuss these blocks in varying detail. To begin with, however,we must specify the tools with which we work. None of these devices arenewwe describe them only for the convenience. They include the fourbasic gates, the OR, AND, NOR and NAND. Symbols and truth tables fortwo-input devices of these types are as shown in the following table:

The other basic device is called a J-K flip-flop. These are integratedcircuits which have the equivalent of about l8 transistorsinterconnected so as to provide the desired characteristics. The symboland state table (this is a dynamic device, unlike a gate) is shownbelow:

Inputs Initial Output Final Outpu t J K O Q Q Q 0 0 I 0 I 0 0 0 0 I 0 l0 l l 0 0 I O l 0 l 0 I l 0 I 0 I 0 l 0 0 I l 0 l 1 0 l l 0 l l I 0 0 IThe input states determine the change in output states upon receipt of aclock pulse. This is a very versatile device. If both inputs are 0, itdoes not switch, whatever state it is in. If one 'input is I, it mayswitch out of one state into the other depending on its state prior toreceiving a clock pulse. If both inputs are 1, it will produce ahalf-frequency square wave at each output.

A considerably expanded block diagram is given in FIG. 13.

INPUT TRIGGER SELECTOR To drive the main translator, this circuitproduces a Ix frequency clock (pulse train) in the low-resolution modeand a fix frequency clock in the high-resolution mode. In the L0-resolution mode, Inverter l-3 has output 1, since its input is 0.AND-gate l-3 then has a 1 input and so reproduces all clock pulses fromsource 1-6 in its output. Flip-flop E (1-5) produces a Ax square wavedescribed and drives AND-gate 1-2. However, 1-2 has one input 0 and thusmaintains an 0 output. Therefore, OR-gate l-4 reproduces all clockpulses. In the I-Ii-resolution mode, Inverter I-3 has output 0 (inputsis I); therefore, AND-gate l-l has 0 output. AND-gate l-2 and OR-gatel-4 will simply reproduce the waveform of flip-flop E. However, thetranslator flip-flops A & B will switch only every other clock pulse.

TRANSLATOR This syste n has the two-line, forward-reverse binary leveland the clock input from the previous circuit as inputs. It producesdirectional control signals which drive the state interpolator andoutput state driver. We will go through one of the four modes (high andlow resolution, forward and reverse), in this case high resolution,forward. The others can be described similarly. Note that, if F=l R=0and vice versa, and that for any flip-flop, if Q is 0, Q is l and viceversa Also note that logic 0 enables the forward and reverse directions,not logic 1. Thus F=0, R=l in this case. Note further that the majorstates change only at every other input clock pulse from the pulsesource I-6.

The sequence table for this mode is shown below:

Translator State Table 0 Step 2-1 2-2 2-3 2-4 2-5 2-6 2 1 2-11 1 o 1 1 1o o 1 1 1 0 o 1 1 1 o 1 1 1 o o s o 1 1 1 1 1 1 o o s o 1 1 1 0 1 1 1 oo 1 1 1 o 1 1 1 High Res-FWD (F=0 2-9 2-10 2-11 2-12 Before After 1.1 K11- n 04 Q- 01 Q- o 1 1 o o o o 1 1 o 1 o o o o 1 1 o 1 o 0 1 1 1 1 o o 11 1 1 1 1 o o 1 1 1 1 o o 1 o 1 1 1 1 o o 1 o 1 1 o o o 0 1 1 o o o o 0As can be seen, the outputs describe a closed cycle. This mode can benow followed through the rest of the circuit.

STATE INTERPOLATOR This circuit takes the output states from thetranslator and the Ix frequency clock pulses and produces intermediatestates. As is evident, it does not differ from the outputs of thetranslator, except that it shifts state on odd-numbered rather thaneven-numbered clock pulses.

HIGH-LOW RESOLUTION SELECTOR To continue with the example, this acceptsthe state interpolator output and the resolution level (I for high, 0for low) to produce half of the driver inputs. The output states areshown in the following table:

ponding to flop 35 into iiiis'zejriiis'miifim voltage starts theacceleration-deceleration circuit 22 which integrates upward at apredetermined rate and clamps at a voltage corres the maximum speedlevel. The voltage-controlled pulse generator 23 now delivers pulses atan increasing rate to the AND-gate 24. The start cycle pulse also resetscounter 34, so that its end of cycle output line is at 1, representingcount not complete. Gate 24 therefore transmits the control pulses tothe translator 25. This is a nonreversing translator, and is Ill-ll.

Low Res. Mode State Clock 30. When it is time to begin o lllloooappreciably simpler than the one shown as item 2 of FIG. 12, which hasreversing capability. The state table is shown below:

High Res. Mode State OUTPUT STATE DRIVER This combines signals from thetranslator and the previous selector to produce output states in ahigh-resolution mode as shown in the following table:

The translator drives the high-resolution interpolator 26, 27, 28, whichis held in the low mode by flip-flop 36. The inter polators output statedriver 28 drives the power amplifiers 29 which in turn drive the motorThis produces a series of states which will rotate the motor indeceleration, the fixed count remaining gate switches,

Mo l-34567 S electrical degree steps. (As it happens this sequence is 30resetting flip-flops 33 and 36. Flip-flop 36 throws the high-lowbackwards; the motor will run in the opposite direction to thatresolution selector 27 in the high-resolution mode so that the in Table3, but we can cure that by enabling R instead of F.) It tor steps arehalf as large. Flipflop 33 drops the input level s P ss y Similarreasoning, to derive the State tables to the acceleration-decelerationcircuit 22 to a low value so the other 3 modes. The table for FWD-Low isshown below: h 22 must integrate downward, d i h voltage m h In K State8 mm m m n m .m.m C Sn t .1 e m ucm w um r. S fwnfl w wbmml wwte p cgm 6m .m.m emw om m m mo -m e m u me d e m [.M m mwc m am 3.3k .1. 1m m 06 1. ts aowaw wm m n u ms mw a e S wP m wmu P 98101 g at least twopoles,

g with two input points said control circuit comg power to the two inputpoints "8 preset number on nown increment of motor rotation.Acceleration and deceleration is provided by controlling the analoginput voltage to a voltage-controlled pulse generator.

Clearly, a full motor cycle is achieved every 4 steps since the 0 inputdisables the state interpolator output and the translator now receivgesa pulse for every input clock pulse.

UN lDIRECIIONAI. OPEN LOOP POSITION SYSTEM Operation of this systemdepends on generating a pulse train whose number of pulses correspondsto a the counter. Each pulse corresponds to a k mi. nmfm nw Mr W 6 no 8mm l1 00000 3 Wm mm. t u C0000 0 0. Pm m 00000 m e A00 000 NH Bm D md Am.m d r 6 m W 5 6 -.re g ne S MSO m .m W 10 M t m sm n S Wnfp .1 n U 6 S0 05 u m u C d u t l 5 s w e P 6 m n .1

The operation is as follows: it is desired to move a s number of motorsteps, which are set on the A majority of steps will be full steps (l.8ventional ZOO-step motor) but a fixed number of ste the decelerationcommand will be half ste transfer into the high-resolution mode. Thehigh-resolution mode in this case is used to obtain more accuratewithout compromising slewing speed. The counter 34 is set to the desiredtotal number of steps and the residual count gate 35 is set to asuitable number of highing,

The start cycle button 21 is then actuated which sets flipmeans forselectively energizing the windings in accordance with the followingsequence:

means for introducing a predetermined plurality of signals to saidcontrol circuit and means for initially applying

1. A circuit for controlling a motor having at least two poles, eachpole having a bifilar winding with two input points thereby providingfour input points, said control circuit cOmprising means for selectivelyapplying power to the two input points of the two poles in accordancewith the following sequence: A B C D 0 1 0 1 0 0 0 1 1 0 0 1 1 0 0 0 1 01 0 0 0 1 0 0 1 1 0 0 1 0 0 wherein A and B are the two input points ofone winding and C and D are the two input points of the other winding,means for selectively energizing the windings in accordance with thefollowing sequence: A B C D 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1means for introducing a predetermined plurality of signals to saidcontrol circuit and means for initially applying power in accordancewith the first-mentioned mode and thereafter applying power inaccordance with the second-mentioned mode, said means being operable toswitch to operation by the secondmentioned mode when a predeterminednumber of said plurality of pulses is remaining.
 2. The control circuitset forth in claim 1 including directional control means for changingthe sequence of application of power to reverse the rotation of themotor.